(a) Technical Field
The present disclosure relates to an automatic transmission for a vehicle.
(b) Description of the Related Art
Recently, increasing oil prices have triggered stiff competition in enhancing vehicle fuel consumption. Research on achieving more shift-stages for an automatic transmission has been undertaken to enhance fuel consumption and drivability.
In particular, to simultaneously provide better drivability and enhanced fuel consumption by achieving more engine shift stages engine, research has been undertaken to reduce engine and to enhance fuel consumption by so-called downsizing of an automatic transmission.
Previously, to achieve more shift stages for an automatic transmission, the number of parts has typically been increased, thereby reducing the ease of installation, increasing production cost, increasing weight and/or decreasing power flow efficiency.
Therefore, in order to maximally enhance fuel consumption of an automatic transmission vehicle having more shift stages, it is important for better efficiency to be achieved using a smaller number of parts.
In this respect, an eight-speed automatic transmission has been recently introduced, and a planetary gear train for an automatic transmission enabling more shift stages is under investigation.
An automatic transmission of eight or more shift-stages typically includes three to four planetary gear sets and five to seven engagement elements (frictional elements), and may easily become lengthy, thereby reducing ease of installation.
Therefore, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements has been attempted. However, such an arrangement may not be widely applicable, and using dog clutches may easily deteriorate shift-feel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.